Fascia Bolt

What a fascia bolt is

A fascia bolt is a short hex bolt with its nut, sold as a kit for fixing fascia purlins: the steel section that runs along the edge of a shed or steel framed roof. Hobson lists the class 4.6 kits with its purlin bolts and the class 8.8 kits in its high tensile range. Its M12 fascia bolts have the 24mm across-flats head that Hobson calls the industry standard.

The class 4.6 assembly is a property class 4.6 bolt, a washer and a class 5 nut. The class 8.8 assembly is a property class 8.8 bolt and a class 8 serrated flange nut, with no separate washer. Hobson publishes no load capacity for these assemblies: the bolt class, size and number of bolts come from the shed maker's or engineer's design, so use what the drawings or kit instructions call for.

Fascia bolt sizes and dimensions

Every fascia bolt we carry. Select a row to open that assembly.

Fascia bolt tightening torque

Hobson gives these indicative torques for use only where the specifying engineer or fascia supplier gives no tightening torque. They are for these seven assemblies only. Torque is worked out as T = P x k x D, where P is a bolt tension of 50% of the bolt's proof load, k is 0.22 for zinc plated and 0.25 for hot dip galvanised assemblies, and D is the thread diameter. The k value changes with thread condition, lubrication and site conditions, and the required tension and torque should be validated by the engineer.

Class 4.6 or class 8.8?

Use the class the design specifies. Class 8.8 is the high tensile bolt and comes here only hot dip galvanised, with a serrated flange nut; class 4.6 comes zinc plated or hot dip galvanised, with a washer and class 5 nut. Do not swap a class 8.8 bolt for a class 4.6 one, and replace like with like when you repair a frame.

Zinc plated or galvanised: where each suits

Hobson rates zinc plating (about 5 microns) as low corrosion resistance, recommended for indoor and non-corrosive environments, and hot dip galvanising (about 50 microns) as high, recommended for long term outdoor use.

Hobson's corrosion guide for metal connectors sets the minimum by exposure. Zinc plated suits only enclosed positions (inside the building envelope) in very low and low corrosion zones. Sheltered positions (out of the rain but open to the air) need galvanised at least in low corrosion areas, and in coastal or industrial areas galvanised with a seal coating, or stainless steel. Positions open to the weather (exposed) need hot dip galvanised or stainless steel, and within 2m of a pool or in seaspray zones stainless steel is the minimum (316 near a pool) even when sheltered. A fascia purlin on the outside edge of a shed is usually sheltered or exposed, so choose hot dip galvanised fascia bolts there, and ask about stainless options near the sea. A newer hot dip galvanised bolt may look duller grey than older bolts; Hobson notes the brightness has no effect on performance.

Fitting fascia bolts

1. Make the holes to the size in AS 4600 or as the designing engineer specifies.
2. Put the bolt through square to the steel: Hobson warns against a skewed bolt.
3. On class 4.6 assemblies fit the washer under the nut; on class 8.8 the serrated flange nut bears straight on the steel.
4. Make sure the underside of the head and the nut (or washer) sit in full contact with the steel.
5. Tighten to the engineer's or fascia supplier's torque, or Hobson's indicative torque above where none is given.

Fascia bolts in Adelaide

Allmat supplies fascia bolts, purlin bolts, nuts, washers and tek screws to shed builders, steel erectors and fabricators across Adelaide and South Australia. Add them to a quote with the rest of your list, and we will price the lot.

Questions